Process for making copper-iron powder



United States Patent rnocnss FGR MAKING COPPER-IRON POWDER Marion Ernest Graham, Parma, and William A. Reed,

West Richfield, Ohio, assignors to Republic Steel Corgoration, Cleveland, Ohio, a corporation of New ersey N Drawing. Application December 29, 1953, Serial No. 401,064

5 Claims. (Cl. 75-.5)

This invention relates to a process for making articles consisting essentially of copper and iron and having high tensile strength and high density, and more particularly to a process for making copper-iron powder, from which such articles may be fabricated by powder metallurgy methods.

This case is related to the co-pending application of Marion Ernest Graham and William A. Reed entitled Copper-iron Powder and Process for Making Same, Serial No. 401,063, filed December 29, 1953. This copending application discloses a method for making copperiron powder by the reduction of certain iron and/ or copper compounds by hydrogen. The supplying of gaseous hydrogen chloride from an external source during reduction is not a necessary feature of that invention. The line of division between the invention of that application and the present invention resides in the fact that the present invention relates to the production of copperiron powder by a hydrogen reduction step effective on iron oxide plus a source of copper wherein HCl gas must be supplied from an external source during the reduction.

High tensile strength and high density articles consisting essentially of copper and iron have found numerous industrial applications, notably in the manufacture of turbine blades and other parts subject to heavy wear and stress, and thusrequiring high tensile strength. In the past, such parts have been produced by such methods as infiltration of molten copper into iron parts previous ly prepared by powder metallurgy methods, and/or the coining of parts made from mixtures of copper and iron powders. While such methods may be effective in producing articles having a high tensile strength, they are ob jectionable in that they involve substantially more complexity and expense of operation than do the relatively simple powder metallurgy processes.

It is an object of this invention, therefore, to provide a process for making articles of high tensile strength t and high density consisting essentially of copper and iron that utilizes the relatively simple methods of powder metallurgy.

It is a further object of the invention to provide a process for making copper-iron powder, which is capable of being formed into articles having a high tensile strength and high density, by processing and sintering and without the necessity of infiltration, coining or similar operations.

Other objects of the invention will be in part apparent and in part pointed out in the following detailed specification.

The process of the invention may be carried out by co-reducing iron oxide with one or both of the hydrogenreducible oxides of copper, such as CuO or CuzO. in-v stead of copper oxide, metallic copper may also be employed. The reduction is carried out by hydrogen or by a reducing gas containing hydrogen as its essential active reducing ingredient. It has been found in accordance with the present invention that in order to produce a copper-iron product having the desired physical properties, hydrogen chloride gas must be present while the reduc- "ice tion reaction is taking place. As either copper oxide or metallic copper are the sole source of copper in accordance with this invention, hydrogen chloride must be supplied from some external source and may be introduced into the reducing zone mixed with the reducing gas.

In some cases it may be desirable to produce a metal powder having some predetermined carbon content. To this end it may be necessary to add a small amount of carbon (e. g. about 1%) to the starting material. The ingredients of the starting material, namely, the iron oxide and the copper-containing material, i. e., copper oxide or metallic copper, are preferably provided in finely divided form, as this assists in attaining one object of the invention, i. e. to produce a material useful in powder metallurgy. These ingredients are mixed together in the proportions that will result in the desired ratio. of iron to copper in the reduced product. The starting material is introduced in a reducing zone, wherein it is contacted with a reducing gas containing hydrogen. It has been found that a powder consisting essentially of about iron and 15% copper is highly desirable for the production of high strength parts. The present invention is, of course, equally applicable for the production of powder having any desired ratio of iron to copper. The solid starting material and the reducing gas are both maintained at an elevated temperature, generally in the range of about 1000 F. to about 1800 F. and contact between them is continued until the reduction of the iron oxide and the other hydrogen-reducible compound (if such a compound be used as the copper-containing material) has been substantially completed. The resultant reaction solid products are then cooled and, in the event that they are in a massive or semi-sintered condition, are comminuted to powder, which is the desired product of the present process.

This copper-iron powder may then be pressed to selfsustaining masses of predetermined size and shape, which are subsequently sintered in a suitable non-oxidizing atmosphere at a temperature of about 2000 F.

The physical properties of the resultant articles will, naturally, be in part dependent upon the ratio of iron to copper contained therein, the pressure at which the powder was molded, the sintering temperature and other factors; but in all cases the product of the present invention will have higher tensile strength than conventional copper-iron parts of the same chemical composition which have been pressed and sintered under the same conditions.

Summarizing the present invention, copper-iron powder suitable for use in powder metallurgy for forming articles having high tensile strength and high density may be produced by introducing into a reducing zone a starting material the essential ingredients of which consist of: (1) iron oxide and (2) copper, in at least one form selected from the group consisting of (a) metallic copper and b) the oxides of copper; and contacting said starting material, in the presence of separately supplied hydrogen chloride, and at an elevated temperature, with a reducing gas containing hydrogen as an essential active reducing ingredient, for a time and under conditions sufiicient to reduce the iron content of said iron oxide to an oxidation state of zero.

The ingredients used for the starting material must include a copper-containing ingredient and iron oxide. The copper-containing ingredient is one or more materials selected from the group consisting of metallic copper and the hydrogen-reducible oxides of copper, i. e., CuO and CuzO. Metallic copper may be derived from any desired source, provided that it is present in a form sufliciently finely divided so that it may be thoroughly mixed with iron oxide. In practice, it has been found that copper powder having an average particle size of about 10 copper and iron or both.

microns is satisfactory, but the copper need not be this 7 finely divided to be useful or fully operative in the process. All that is required is that the copper have a particle size sufficiently small to insure the productionof a substantially homogeneous mixture as the starting material. The same consideration is controlling with regard to the particle size of all other ingredients of the starting material.

If the copper-containing ingredient of the starting material is copper oxide, it is immaterial insofar as the operation of the present invention is concerned, whether it be in the cupric or cuprous state. It is believed that when cupric oxide is reacted with an agent capable of reducing it, it is initially converted to cuprous oxide as an intermediate stage in the reduction to metallic copper. Whether these theories be accurate or not, it has been found that the cuprous and cupric forms of the oxide are equally effective; and as such, are the equivalents of one another for the purpose of the present invention.

It is to be understood that the term copper oxide as such herein and in the appended claims is further meant to include those copper compounds which decompose easily under the influence of heat to form oxides. Examples of such compounds are acetates, oxalates, formates and similar organic salts. Since such compounds quickly form oxides when heated, they are believed to be so converted in the reducing zone before reduction proper actually begins, and so may be considered chemical equivalents of copper oxide.

The iron oxide which forms'the iron-containing ingredient of the starting material may be any iron oxide that is relatively easily reduced by the action of hydrogen. Either Fe2O or F6304 may be employed interchangeably, or mixtures of them may be used if desired. Ferrous oxide (FeO) may also be'employed as a starting material, although its chemical instability renders it' somewhat'difncult to preserve in this form. However, since all hydrogen-reducible iron oxides are equally effective, mixtures containing some FeO may be employed.

The thoroughly mixed starting materials may be placed in a suitable container, such as a metal boat or pan, and introduced into a reducing zone, wherein the hydrogen-reducible materials present are reduced. In order to insure maximum yield, based on the amount of raw material used, it is necessary that the chemical reaction be carried to substantial completion. By this it is meant that the metallic constituents of the hydrogen-reducible compounds present he reduced to an oxidation state of zero. This phrase, as used in the description and in the appended claims, is meant to embrace both the production of either a physical mixture of the elemental materials in powder form or the production of some alloy of In any case, the metallic constituents are present in an oxidation state of zero, as opposed to some positive oxidation state which they had initially when present in the form of the respective chemical compounds, such as iron oxide, copper oxide, etc.

The conditions of reduction are not critical to the success of the process, except that they must be sufiicient as to both time and temperature to insure substantially complete reaction between the iron oxide and the hydrogen-reducible copper compound (if one be employed) and the hydrogen-containing reducing gas. In practice it has been found that temperatures of at least about 1000 F. are desirable to insure reduction of the iron oxide in a reasonable time period, namely about two or three hours. Lower temperatures may be employed, but only by using substantially longer times, which is usually considered economically impracticable. more readily reducible than is iron oxide, the reduction of copper to an oxidation state of zerois insured when the iron content of the iron oxide is reduced to this same oxidation state. Unduly high reduction temperatures 'may cause the production of a hardrsinter ed product,

which-will be difiicult to grind; and this is to be avoided,

Since copper oxide is much since one of the objects of the present invention is the production of a pulverulent material, which may be used in conventional powder metallurgy processes. it has been found, however, that temperatures of up to about 1800" F. will result in the production of a material which is quite frangible and thus may be comminuted to powder without undue trouble or expense.

An essential feature of the present invention is the presence, during the reduction reaction, of hydrogen chloride in the reducing zone. In accordance with the present invention metallic copper or copper oxides are employed, so that the hydrogen chloride must be supplied to the reducing zone from some external source. This is generally done by mixing hydrogen chloride gas directly with the hydrogen-containing reducing as. it

has been found in practice that direct mixing of the hydrogen chloride with the reducing gas is the most practical method of insuring the presence of hydrogen chloride. it has been found that small concentrations of hydrogen chloride in the reducing gas are sufiicient to produce the desired results. A concentration of about 1% hydrogen chloride by volume based on the total volume of hydrogen and hydrogen chloride present in the reducing gas has been found to be suflicient, although no adverse eifects, and in some cases slight improvements, are obtained by using up to about 4% hydrogen chloride by volume calculated in the same way. The presence of inert ingredients, such as nitrogen, in the reducing gas may be tolerated as it is not deleterious to the process of the invention. The measure of what gases are inert as that term is used herein is determined by what gases may be present without substantially interfering with the desired reduction reactions as herein set forth.

The presence of hydrogen chloride in the reduction zone is essential for the production of the desired copperiron powder. As will be pointed out in subsequent examples, copper-iron parts made from powder produced under conditions corresponding exactly to those required and herein taught in accordance with the present invention, except that hydrogen chloride is not present, are definitely inferior to those produced by the process of the present invention.

After the reduction reaction has been substantially completed, the reduced powder is cooled in a non-oxidizing atmosphere to a temperature of about 200F., or less. The resultant mass may then be comminuted to powder of the desired particle size or size range, this powder being subsequently used in various powder metallurgy processes, according to standard practice.

Example I rials were spread on a tray to a depth of about A 'inch.

The loaded tray was sealed in an electrically heated mufiie furnace. The gas having a composition as aforesaid was passed through the furnace over the surface of the mixture and the temperature of the contents of the furnace was maintained at about 1200" F. The sealed inner tube of the furnace was then removed from the heating muifie and the contents allowedto cool toa temperature below 200 F. The completelyreduced copper-iron product which had formed into a semi-sintered, but easily frangible, cake was then ground to a particle size of about -100 mesh. The powder was found by chemical analysis to contain 15% copper and iron.

This powder was mixed with 1% zinc stearate as a lubricant, pressed at 50,000 p. s. i. to form a standard test bar, which was sintered in hydrogen at 2,000 F. for one hour. The resulting piece had a tensile strength of 74,900 p. s. i.

A test bar prepared under identical conditions of pressing and sintering from a mixture of flake copper and Commercial iron powder (made by the reduction of iron oxide) in the proportion of 85% iron and copper, had a tensile strength of only 34,300 p. s. i. A subsequent coining or similar reworking operation would be necessary to raise the strength of this latter piece to an acceptable value; but such strength is readily obtained in accordance with the process and by the use of the powder (product) of the present invention by the use of simple powder metallurgy techniques.

This reducing, pressing and sintering procedure was repeated on the same starting material, except that the reducing gas contained 4% HCl by volume. The bar thus produced had a tensile strength of 69,200 p. s. i. and a density of 7.48 grams per cubic centimeter. Since the density of pure iron is only about 7.86 grams per cubic centimeter, it will be seen that the theoretical maximum density for this particular composition is approached by using the method of the present invention.

When pure hydrogen, containing no hydrogen chloride, was employed as the reducing gas, a test bar produced from the identical starting material had a tensile strength of only 45,200 p. s. i. and a density of only 6.47 grams per cubic centimeter. A comparison of these results indicates the novel, unexpected and highly useful results flowing from the presence of hydrogen chloride in the reducing zone during the reduction.

Example 11 A mixture of FezO; and copper oxide (CuO) was reduced, and the resulting powder pressed and sintered in the manner previously described to produce a test bar containing 15 copper and the balance iron.

The reducing gas contained 98% hydrogen and 2% HCl by volume. This test bar had a tensile strength of 82,500 p. s. i. When the procedure was repeated on the same starting material using pure hydrogen (no HCl) as a reducing gas, the test bar produced had a tensile strength of only 59,400 p. s. i. The eflect of the presence of hydrogen chloride in the reducing gas for attaining strength is again indicated.

While there have been disclosed herein several specific process and certain variants thereof, other alternatives and equivalents will occur to those skilled in the art from the foregoing disclosure. We do not wish to be limited, therefore, except by the scope of the appended claims, which are to be construed validly as broadly as the state of the prior art permits.

What is claimed is:

1. The process of making copper-iron powder suitable for use in powder metallurgy for forming articles having high tensile strength and high density, comprising the steps of introducing into a reducing zone a starting material, the essential ingredients of which consist of: (1) iron oxide, and (2) copper, in at least one form selected from the group consisting of (a) metallic copper and (b) the oxides of copper; and contacting said starting material at an elevated temperature, with a reducing gas containing hydrogen as an essential active reducing ingredient and for a time and under conditions suflicient to reduce the iron content of said iron oxide to an oxidation state of zero and supplying gaseous hydrogen chloride to said zone for contact with said starting material therein substantially throughout the reduction of the hydrogenreduceable material in said zone.

2. The process according to claim 1, wherein the copper-containing ingredient of said starting material is metallic copper.

3. The process according to claim 1, wherein the copper-containing ingredient of said starting material is copper oxide.

4. The process of making copper-iron powder suitable for use in powder metallurgy for forming articles having high tensile strength and high density, comprising the steps of introducing into a reducing zone a starting material the esssential ingredients of which are iron oxide and copper, also introducing into said zone a reducing gas containing hydrogen as its essential active reducing ingredient and also containing at least about 1% by volume of hydrogen chloride (based on the total volume of hydrogen and hydrogen chloride) and maintaining the materials aforesaid in said zone at a temperature of at least about 1000 F. for a time suflicient to reduce the iron content of said iron oxide to an oxidation state of zero.

5. The process of making copper-iron powder suitable for use in powder metallurgy for forming articles having high tensile strength and high density, comprising the steps of introducing into a reducing zone a starting material the essential ingredients of which are iron oxide and copper-oxide, also introducing into said zone a reducing gas containing hydrogen as its essential active reducing ingredient and also containing at least about 1% by volume of hydrogen chloride (based on the total volume of hydrogen and hydrogen chloride) and maintaining the materials aforesaid in said zone at a temperature of at least about 1000 F. for a time suflicient to reduce the iron content of said iron oxide to an oxidation state of zero.

References Cited in the file of this patent UNITED STATES PATENTS 2,200,369 Klinker May 14, 1940 2,279,013 Roseby Apr. 7, 1942 2,651,105 Neel Sept. 8, 1953 FOREIGN PATENTS 473,238 Great Britain Oct. 8, 1937 506,432 Great Britain May 30, 1939 642,773 Great Britain Sept. 13, 1950 644,813 Great Britain Oct. 18, 1950 655,995 Great Britain Aug. 8, 1951 672,354 Great Britain May 21, 1952 

1. THE PROCESS OF MAKING COPPER-IRON POWDER SUITABLE FOR USE IN POWDER METALLURGY FOR FORMING ARTICLES HAVING HIGH TENSILE STRENGTH AND HIGH DENSITY, COMPRISING THE STEPS OF INTRODUCING INTO A REDUCING ZONE A STARTING MATERIAL, THE ESSENTIAL INGREDIENTS OF WHICH CONSIST OF: (1) IRON OXIDE, AND (2) COPPER, IN AT LEAST ONE FORM SELECTED FROM THE GROUP CONSISTING OF (A) METALLIC COPPER AND (B) THE OXIDES OF COPPER; AND CONTACTING SAID STARTING MATERIAL AT AN ELEVATED TEMPERATURE, WITH A REDUCING GAS CONTAINING HYDROGEN AS AN ESSENTIAL ACTIVE REDUCING INGREDIENT AND FOR A TIME AND UNDER CONDITIONS SUFFICIENT TO REDUCE THE IRON CONTENT OF SAID IRON OXIDE TO AN OXIDATION STATE OF ZERO AND SUPPLYING GASEOUS HYDROGEN CHLORIDE TO SAID ZONE FOR CONTACT WITH SAID STARTING MATERIAL THEREIN SUBSTANTIALLY THROUGHOUT THE REDUCTION OF THE HYDROGENREDUCEABLE MATERIAL IN SAID ZONE. 